The invention relates to a process for setting a thermal trip device with bimetal strip, notably for an electrical circuit breaker, consisting in positioning the bimetal strip in relation to an adjusting pin of a trip bar, following input of a setting current of an intensity greater than that of the rated current.
There are a multitude of environmentally linked constructional parameters liable to influence the behaviour of a thermal trip device with bimetal strip. The cumulated sum of the tolerances generated by these parameters can be greater than the tripping range imposed by the standard, which specifies that tripping must take place between 1.05In and 1.3In after one hour (In being the rated current).
Factory setting serves the purpose of minimizing the influence of these parameters, and consists in fixing the relative positions of the bimetal strip with respect to the tripping basis.
A state-of-the-art factory setting method consists in applying a monitoring current of 3In for a preset fixed time. An adjustment screw then enables the foot of the bimetal strip to be deformed to trip the circuit breaker.
Another state-of-the-art method uses a wedge, which after the current has been applied for a fixed time, is secured to the bar by means of a glue sensitive to ultra-violet radiation. Polymerization of the glue takes several seconds, during which period it is indispensable to immobilize the position of the bimetal strip in relation to the trip bar. The time taken by such a setting cycle is very long, which constitutes a drawback when setting is carried out on an automatic production line.
In these prior art methods, monitoring of the initial position of the bimetal strip is based exclusively on the current flow during a given time.
A first object of the invention consists in improving the factory setting process of a thermal trip device in order to overcome all the external or constructional factors of influence.